The present invention is directed to a non-electrical thermo-mechanical boiler control system for simultaneously controlling fuel and air supply to a burner in dependence on the temperature difference between forward water to the radiators and return water from the radiators of a hot-water heating installation having thermostatic radiator valves associated with each of the radiators.
In the prior art such as German patent application No. P 2948797.6 filed by F. Salzmann, December 1979, there is disclosed an electronic system for controlling an on-off mode the burner for a boiler. The electronic control system for regulating the water temperature in the domestic boiler heating system which has valve controlled radiators, measures the difference between forward-flow temperature and return-flow temperature of the hot water and feeds it into a microcomputer to control the on-off switching of the burner. In the U.S. Pat. No. 4,294,402, assigned to the same assignee as the present invention, the temperature difference between forward water temperature and return water temperature is used to control a mixing valve but not to control the burner itself.
In the present invention a modulating burner has both the air supply and the fuel supply controlled in dependence on the temperature difference between forward water temperature and return water temperature.